Meteorological device employing a temperature compensated transmitter

ABSTRACT

This invention relates to a meteorological device that is used to transmit atmospheric conditions such as temperature, pressure, humidity, or the like, to a remote station. The transmitter of such device utilizes temperature-compensating means with a highfrequency transistor oscillator thereby obtaining a highly stable output over a wide temperature range. Temperature compensation is provided by mounting the transistor directly onto dual resonant coaxial cavities with one cavity connected to the transistor emitter and the other cavity connected to the base lead. The cavities are constructed of dissimilar metals thereby providing temperature dependent capacitance. The cavities are provided with sets of adjusting screws to provide for adjustments in cavity resonance brought about by both lateral and transverse unequal expansion in the cavities.

United States Patent Inventors Robert E. Askew Berkeley Heights; HenryC. Johnson, Neshanic, NJ.

803,156 Feb. 28, 1969 May4, 1971 Appl. No. Filed Patented Assignee b'mesecrewyarimm METEOROLOGICAL DEVICE EMPLOYING A The United Statesor'ariie r'as gggg r'gsg e TEMPERATURE COMPENSATED TRANSMITTER PrimaryExaminer-John Kominski Attomeys-Harry M. Saragovitz, Edward J. Kelly,Herbert Berl and Jess J. Smith, Jr.

ABSTRACT: This invention relates to a meteorological device that is usedto transmit atmospheric conditions such as temperature, pressure,humidity, or the like, to a remote station. The transmitter of suchdevice utilizes temperature-compensating means with a high-frequencytransistor oscillator thereby obtaining a highly stable output over awide temperature range. Temperature compensation is provided by mountingthe transistor directly onto dual resonant coaxial cavities with onecavity connected to the transistor emitter and the other cavityconnected to the base lead. The cavities are constructed of dissimilarmetals thereby providing temperature dependent capacitance. The cavitiesare provided with sets of adjusting screws to provide for adjustments incavity resonance brought about by both lateral and transverse unequalexpansion in the cavities.

BACKGROUND AND SUMMARY OF THE INVENTION Rocketand balloon-carriedscientific instruments have seen wide utility for a number of years ingathering meteorological data of the upper atmosphere. Since thedatagathering package, sometimes known as a radiosonde or rocketsonde,is subjected to the rigors of launch or recovery and varyingenvironments, the transmitter placed therein must be ruggedlyconstructed with as stable an output frequency as possible with respectto temperature changes. The device of the instant invention accomplishesthese tasks by providing an improved rocketsonde with substantially flatfrequency response over a wide range of temperatures.

It is the objective of this invention to produce a compact, lightweight,low cost, highly stable L-band solid-state rocketsonde capable ofwithstanding in excess of 75 GS, axial and longitudinal, accelerationand providing an output of approximately one-fourth watt.

Earlier work in this particular field has employed various techniquesincluding the use of a single cavity oscillator followed by a multipliersection to attain the desired frequency. Likewise, another typeradiosonde has been constructed using the stripline oscillator; however,this approach has not been entirely successful. Inasmuch as the deviceof the instant invention employs a fundamental frequency oscillator,there is no multiplication effect of frequency change occasioned by avariation in supply voltage. Here also, two resonant cavities are usedto increase the effective and thus improve transmitter pulling figure.

BRIEF DESCRIPTION OF THE DRAWING The exact nature of this invention willbe readily apparent from consideration of the following specificationrelating to the annexed drawing in which:

FIG. 1 shows a partial sectional view of the preferred embodiment of theinvention;

FIG. 2 illustrates a diagram of one circuit used with the cavities ofFIG. I; and

FIG. 3 shows the performance curves of the rocketsonde transmitter ofthe instant invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings,wherein like reference characters designate like or corresponding partsthroughout the several views, there is shown in FIG. I a partial crosssection of the cavity oscillator used in the rocketsonde to transmitatmospheric conditions such as temperature, pressure, humidity or thelike to a remote station. There is shown housing 11 containing cavities12 and 13. Mounted inside each of the cavities l2 and 13 are two centerconductors I4 and 15. Transistor 16, having base 17 and emitter 18leads, is mounted directly onto housing 11. Since a high-frequencytransistor oscillator normally has a negative temperature coefficient,that is, its oscillating frequency goes down when the ambienttemperature" goes up, some sort of temperature compensating means mustbe employed to maintain oscillator frequency within desired limits.Temperature compensation in the instant invention is achieved byconstructing the housing 11 and the center conductors 14 and ofdissimilar metals with different thermal coefficients of expansion andby providing sets or pairs of end tuning screws 19 and 20, and sidetuning screws 21 and 22. Housing 11 is constructed of brass or silverplated brass with a coefficient of thermal expansion of approximately18.9)(10 cm./cm. C. while center conductors M and 15 are constructed ofcopper with a coefficient of thermal expansion of approximately I6XIOcm./cm. C. The transistor 16, a TA 2800 transistor has been successfullyemployed, leads 17 and 18 are coupled to center conductors 14 and 15 bymeans of copper coupling sleeves 23 and 24 which have been coated with Imil thick Teflon. The sleeve capacitance and lead impedance form thematching circuit between the transistor .16 and the resonant cavities 12and 13. Coaxial output 26 is provided with output coupling loop 25 tofeed a suitable antenna (not shown).

When an oscillator circuit is connected to the cavities 12, 13 and istuned to resonance using only the capacitance formed between the ends ofthe center conductors 14, 15 and the end tuning screws 19, 20, theoscillator has a positive temperature coefiicient. Conversely, when onlythe side tuning screws 21, 22 are used for tuning to resonance, thedevice has a negative temperature coefiicient. By distributing thecapacitance required for resonance between the end tuning screws 19, 20and the side tuning screws 21, 22, an essentially flat frequency versustemperature characteristic is achieved. The differences in thecoefficients of expansion cause the capacitance formed between the endsof the center conductors 14 and 15 and the end tuning screws 19 and 20,that is, across dimension 1, to decrease with increasing temperaturewhereas the capacitance formed between the center conductors I4 and 15and side tuning screws 21 and 22, that is across dimension t, remainapproximately constant with increasing temperature. If all the requiredcapacitance for resonance is formed by the side tuning screws 21 and 22,the natural tendency of the transistor 16 to cause decreasing frequencyoutput with increasing temperature would predominate. On the other hand,if all the capacitance for resonance is formed by the end screws 19 and20, the oscillating frequency would in- 'f crease rapidly withincreasing temperature. It is obvious, then, that the desired amount ofcompensation can be achieved by distributing the capacitance between thetwo sets of screws 19, 20 and 21,22.

There is shown in FIG. 2 the cavity oscillator 10 described above withthe circuitry employed in constructing the rocketsonde transmitter ofthe instant invention that is capable of producing a highly stableoutput. A grounded collector oscillator circuit is provided with theemitter 18 and base 17 leads capacitively coupled into their respectivecavities 13 and 12. Capacitors in the form of copper sleeves 23 and 24together with the coupling loops formed by leads I7 and 18 provide theproper matching of the transistor into the cavity and also provide DCblocks for the transistor leads 17 and 18. Small quarter wavelengthetched high-impedance RF chokes 43 and 44 are mounted inside each of thecavities l2 and 13 to provide the necessary biasing connections through1,500 pF feedthrough capacitors 49 and 50 mounted in the wall of housing11. A highly stable negative 20 volt DC input voltage is provided at Ithrough a 10 ohm current limiting resistor 41. Base bias resistors 46and 48, 200 and 3.3 k ohms respectively, were employed in the devicesactually constructed with these values varying depending on thedimensions and placement of the transistor lead loops 17 and 18. Forwardbiased silicon diode 45, 1N46l in the circuit constructed, is used toreplace a rather bulky and expensive silicon resistor used in earliertests thereby providing for a more compact and inexpensive transmitter.Since the forward biased diode 45 has a negative temperaturecoefficient, additional temperature compensation is provided in additionto' the current leveling effect in the base-emitter biasing circuit.Frequency modulation is provided by changing the base bias through a 690ohm series resistance 47 at input 1,. When a pulse input of negative 3volts is provided to terminal I the oscillator cuts off therebyproviding for amplitude modulation. Terminal I4 is provided for apositive voltage and housing 11 ground. Variable capacitors 31, 32, 33,and 34 are shown here in FIG. 2 as schematically representing theelectrical characteristics of tuning screws 19, 20, 21, and 22 ofFIG. 1. It may readily seem that inputs I and I; may be employed withatmospheric sensors that are capable of measuring temperature, pressure,humidity, or the like as well as other devices or equipment requiring ahighly stable oscillator over a wide range of temperatures.

Turning now to FIG. 3 we see the performance characteristics for thedevice of the instant invention, and particularly, of the circuitryshown in FIG. 2. For example, it is seen from FIG. 30 that thetransmitter has a frequency variation of less than 2 W2. over thetemperature range of r-70 C. to +70 C. Likewise, the power output andefficiency of the transmitter can be seen from FlGS. ill) and 3crespectively. Although not shown by the above described FlGS. it hasbeen found that the output power, efficiency and pulling figure (thefrequency change for a load VSWR of 1.5 to l which is variable in phasethrough 360 electrical degrees) can he substany improved by than theefi'eetive area at the output coimling. A inn-titer advantage at theinstant device over those at prior art is that the instant invention hasa p i, the sensitivity oil the operudng trerruency to supply voltagemange oi less than one-iourth oi the earlier devices and is imlly lessthan 0.5 lVil-lz. per volt. Spurious output measurements have been madewith the second harmonic measured approximately 40 db. the fundamentaland the third harmonic approximately db. the second harmonic.

Although the cavities l2 and i3 are shown in FlGS. l and 2 as being partof the same housing for purposes of simplicity of description, thecavities actually constructed were formed from a %-inch cylindricalsection for base cavity 112 with the emitter cavity 13 being formed froma lit-inch cylindrical section thereby giving a housing diameter ofapproximately 1 inch with electrical contact therebetween. 'lhe overalllength of the transmitter actually constructed was less than 3 incheswith a weight of less than 3 ounces.

It should be understood, of course, that the foregoing disclosurerelates to only a preferred embodiment of the invention and thatnumerous alterations may be made therein without departing from thespirit and scope of the invention as set forth in the appended claims.

- We claim:

l. A rocketsonde, used for measuring atmospheric conditions having ahighly stable oscillator, said oscillator comprismg:

dual cavities for maintaining oscillator resonance, said dual cavitiesbeing constructed of a material having a coefficient of thermalexpansion and being closely juxtaposed so as to he in electricalcontact;

center conductors mounted inside each of said cavities and fabricated ofa material having a different ooetiicient of thermal expansion than saiddual cavities;

adjusting means for changing the resonant frequency of said cavities andfor maintaining said oscillator at substantially the same frequency asthe rocltetsonde is subjected to various atmospheric conditions whensaid center conductors and said cavities expand and contract at unequalrates;

power supply means connected to said oscillator, and;

output means coupled to one of sa d dual cavities for transmitting to aremote station. 2. The roclcetsonde oscillator according to claim it,and

further comprising:

a transistor mounted on said dual cavities, said transistor having anemitter, collector, and base lead;

said power supply means is connected so as to negatively bias saidemitter;

means for capacitively coupling said emitter to said one of said centerconductors;

means for capacitively coupling the base of said transistor to the otherof said center conductors;

said output means is coupled to the cavity containing said base, and;

means for grounding said collector to said cavities.

3. The rocketsonde oscillator according to claim 2, and

further comprising:

said means for negatively biasing said emitter comprises a currentlimiting resistor connected in series with a feedthrough capacitor in acavity wall and an RF choke mounted inside said cavity containing saidemitter;

means for connecting said cavities and said base through a resistor inseries with a feedthrough capacitor in a cavity wall and an RF chokemounted inside said cavity containing said emitter, and;

current leveling means connected between said means for connecting andsaid negative biasing means.

4. The rocketsonde oscillator according to claim 3, and

further comprising:

said current leveling means comprises a-series-connected resistor andsilicon diode.

5. A highly stable oscillator comprising:

dual resonant cavities fabricated of a material having one coefficientof thermal expansion;

center conductors mounted in each of said dual cavities and fabricatedof a material having a second coefficient of thermal expansion therebyproviding capacitance changes between said center conductors and saidcavities as said center conductors and said cavities unequally expandand contract when subjected to temperature changes, and

a transistor oscillator circuit connected to said cavities in such amanner that said transistor base is capacitively coupled to one of saiddual resonant cavities, said transistor emitter is capacitively coupledto the other of said dual resonant cavities and to a negative powersource, and said transistorcollector is grounded to said dual resonantcavities thereby producing a highly stable transistor oscillator.

d. A device for use in a highly stable oscillator, that is subject tovarying environmental conditions, comprising:

a pair of cylindrically shaped cavities each having wall, en-

closed ends, and a longitudinal axis, said cavities being constructed ofa material having a first coefficient of thermal expansion, saidcavities being placed adjacent to each other and in electrical contact;

center conductors having first and second ends mounted inside said dualcavities with said first end in electrical contact with said cavity endsand parallel to the longitudinal axes thereof, said center conductorsbeing fabricated of a material having a second coefficient of thermalexpansion so that the capacitance between said cavities and said centerconductors is divided between said cavity ends and said second end ofsaid center conductors and between said cavity walls and said second endof said center conductors as said center conductors and said cavitiesunequally expand and contract as said device is subjected to varyingenvironmental conditions.

7. The resonant device according to claim 6 and further comprising:

sets of adjusting screws mounted in the ends of each cavity and in thewalls of each cavity adjacent to the second ends of said centerconductors for distributing the capacitance required for resonancebetween the second end of said center conductors and the ends of saidcavities and between the second end of said center conductors and saidcavity walls thereby giving said oscillator an essentially flatfrequency versus temperature characteristic.

8. A dual coaxial transistor oscillator that is highly stable over awide range of environmental conditions comprising:

a pair of cylindrically shaped cavities each having walls, en-

closed ends, and a longitudinal axis, said cavities being constructed ofa material having a first coefficient of thermal expansion, saidcavities being placed adjacent to each other and in electrical contact;

center conductors having first and second ends mounted inside said dualcavities with said first end in electrical contact with said cavity endsand parallel to the longitudinal axis thereof, said center conductorbeing fabricated of a material having a second coefficient of thermalexpansion so that the capacitance between said cavities and said centerconductors is divided between said cavity ends and said second end ofsaid center conductors and between said cavity walls and said second endof said center conductors as said center conductors and said cavitiesunequally expand and contract as said device is subjected to varyingenvironmental conditions;

said cavities thereby providing frequency adjustment means and providingsaid oscillator with an essentially flat oscillating frequency versustemperature characteristics over a wide range range of environmentalconditions. 9. The device according to claim 8, and further comprising:coupling means attached to one of said cavities for transmitting saidoscillations to a remote station.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 315771Dat d 5/ /7 Inventor(s) ROBERT E. ASKEW 8c HENRY C. JOHNSON It iscertified that: error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

column 1, line 68, 18.9 x 10 should read 18.9 x l( and in line 70,316 x10 should read 16 x 1.0

column 3, line 15, "#0 db" should read +0 db below and in line 16, "20db" should read 20 db below claim 0, line 3, "well" should be wallsSigned and sealed this 28th day of November 1972.

(SEAL) Attest:

EDWARD M.FLETC lI-ER JR ROBERT GOTTSCHALK Attesting OfficerCommissionerof Pater

1. A rocketsonde, used for measuring atmospheric conditions having ahighly stable oscillator, said oscillator comprising: dual cavities formaintaining oscillator resonance, said dual cavities being constructedof a material having a coefficient of thermal expansiOn and beingclosely juxtaposed so as to be in electrical contact; center conductorsmounted inside each of said cavities and fabricated of a material havinga different coefficient of thermal expansion than said dual cavities;adjusting means for changing the resonant frequency of said cavities andfor maintaining said oscillator at substantially the same frequency asthe rocketsonde is subjected to various atmospheric conditions when saidcenter conductors and said cavities expand and contract at unequalrates; power supply means connected to said oscillator, and; outputmeans coupled to one of said dual cavities for transmitting to a remotestation.
 2. The rocketsonde oscillator according to claim 1, and furthercomprising: a transistor mounted on said dual cavities, said transistorhaving an emitter, collector, and base lead; said power supply means isconnected so as to negatively bias said emitter; means for capacitivelycoupling said emitter to said one of said center conductors; means forcapacitively coupling the base of said transistor to the other of saidcenter conductors; said output means is coupled to the cavity containingsaid base, and; means for grounding said collector to said cavities. 3.The rocketsonde oscillator according to claim 2, and further comprising:said means for negatively biasing said emitter comprises a currentlimiting resistor connected in series with a feedthrough capacitor in acavity wall and an RF choke mounted inside said cavity containing saidemitter; means for connecting said cavities and said base through aresistor in series with a feedthrough capacitor in a cavity wall and anRF choke mounted inside said cavity containing said emitter, and;current leveling means connected between said means for connecting andsaid negative biasing means.
 4. The rocketsonde oscillator according toclaim 3, and further comprising: said current leveling means comprises aseries-connected resistor and silicon diode.
 5. A highly stableoscillator comprising: dual resonant cavities fabricated of a materialhaving one coefficient of thermal expansion; center conductors mountedin each of said dual cavities and fabricated of a material having asecond coefficient of thermal expansion thereby providing capacitancechanges between said center conductors and said cavities as said centerconductors and said cavities unequally expand and contract whensubjected to temperature changes, and a transistor oscillator circuitconnected to said cavities in such a manner that said transistor base iscapacitively coupled to one of said dual resonant cavities, saidtransistor emitter is capacitively coupled to the other of said dualresonant cavities and to a negative power source, and said transistorcollector is grounded to said dual resonant cavities thereby producing ahighly stable transistor oscillator.
 6. A device for use in a highlystable oscillator, that is subject to varying environmental conditions,comprising: a pair of cylindrically shaped cavities each having wall,enclosed ends, and a longitudinal axis, said cavities being constructedof a material having a first coefficient of thermal expansion, saidcavities being placed adjacent to each other and in electrical contact;center conductors having first and second ends mounted inside said dualcavities with said first end in electrical contact with said cavity endsand parallel to the longitudinal axes thereof, said center conductorsbeing fabricated of a material having a second coefficient of thermalexpansion so that the capacitance between said cavities and said centerconductors is divided between said cavity ends and said second end ofsaid center conductors and between said cavity walls and said second endof said center conductors as said center conductors and said cavitiesunequally expand and contract as said device is subjected to varyingenvironmental conditions.
 7. The resonant deviCe according to claim 6and further comprising: sets of adjusting screws mounted in the ends ofeach cavity and in the walls of each cavity adjacent to the second endsof said center conductors for distributing the capacitance required forresonance between the second end of said center conductors and the endsof said cavities and between the second end of said center conductorsand said cavity walls thereby giving said oscillator an essentially flatfrequency versus temperature characteristic.
 8. A dual coaxialtransistor oscillator that is highly stable over a wide range ofenvironmental conditions comprising: a pair of cylindrically shapedcavities each having walls, enclosed ends, and a longitudinal axis, saidcavities being constructed of a material having a first coefficient ofthermal expansion, said cavities being placed adjacent to each other andin electrical contact; center conductors having first and second endsmounted inside said dual cavities with said first end in electricalcontact with said cavity ends and parallel to the longitudinal axisthereof, said center conductor being fabricated of a material having asecond coefficient of thermal expansion so that the capacitance betweensaid cavities and said center conductors is divided between said cavityends and said second end of said center conductors and between saidcavity walls and said second end of said center conductors as saidcenter conductors and said cavities unequally expand and contract assaid device is subjected to varying environmental conditions; atransistor mounted on said cavities and having a base, emitter, andcollector; said base being capacitively coupled to one of said centerconductors and to the wall of one of said cavities; said emitter beingnegatively biased and capacitively coupled to the other of said centerconductors; said collector being connected to the wall of one of saidcavities, thereby providing oscillations within said cavities; at leastone adjusting screw mounted in the wall of one of said cavities therebyproviding frequency adjustment means and providing said oscillator withan essentially flat oscillating frequency versus temperaturecharacteristics over a wide range range of environmental conditions. 9.The device according to claim 8, and further comprising: coupling meansattached to one of said cavities for transmitting said oscillations to aremote station.